title: Simultaneous analysis of tramadol, O-desmethyltramadol, and N-desmethyltramadol enantiomers in rat plasma by high-performance liquid chromatography-tandem mass spectrometry: application to pharmacokinetics.
abstract: Tramadol (T) is available as a racemic mixture of (+)-trans-T and (-)-trans-T. The main metabolic pathways are O-demethylation and N-demethylation, producing trans-O-desmethyltramadol (M1) and trans-N-desmethyltramadol (M2) enantiomers, respectively. The analgesic effect of T is related to the opioid activity of (+)-trans-T and (+)-M1 and to the monoaminergic action of (+/-)-trans-T. This is the first study using tandem mass spectrometry as a detection system for the simultaneous analysis of trans-T, M1, and M2 enantiomers. The analytes were resolved on a Chiralpak® AD column using hexane:ethanol (95.5:4.5, v/v) plus 0.1% diethylamine as the mobile phase. The quantitation limits were 0.5 ng/ml for trans-T and M1 and 0.1 ng/ml for M2. The method developed and validated here was applied to a pharmacokinetic study in rats. Male Wistar rats (n=6 at each time point) received a single oral dose of 20 mg/kg racemic trans-T. Blood samples were collected up to 12 h after drug administration. The kinetic disposition of trans-T and M2 was enantioselective (AUC((+))/((-)) ratio=4.16 and 6.36, respectively). The direction and extent of enantioselectivity in the pharmacokinetics of trans-T and M2 in rats were comparable to data previously reported for healthy volunteers, suggesting that rats are a suitable model for enantioselective studies of trans-T pharmacokinetics.
authors.affiliation: Departamento de Análises Clínicas, Toxicológicas e Bromatológicas, Faculdade de Ciências Farmacêuticas de Ribeirão Preto, Universidade de São Paulo, Ribeirão Preto, SP, Brazil.
authors.forename: Ana Leonor Pardo Campos
authors.initials: AL
authors.lastname: Godoy
authors.forename: Natália Valadares
authors.initials: NV
authors.lastname: De Moraes
authors.forename: Edson Zangiacomi
authors.initials: EZ
authors.lastname: Martinez
authors.forename: Teresa Maria De Jesus Ponte
authors.initials: TM
authors.lastname: Carvalho
authors.forename: Maria Paula
authors.initials: MP
authors.lastname: Marques
authors.forename: Vera Lucia
authors.initials: VL
authors.lastname: Lanchote
mesh_terms: D000818:Animals; D019540:Area Under Curve; D002851:Chromatography, High Pressure Liquid / Q000379:methods*; D002853:Chromatography, Liquid / Q000379:methods; D008297:Male; D010949:Plasma / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013237:Stereoisomerism; D053719:Tandem Mass Spectrometry / Q000379:methods*; D014147:Tramadol / Q000031:analogs & derivatives* / Q000097:blood* / Q000737:chemistry
chemical_list: C080580:O-demethyltramadol; D014147:Tramadol; C080579:N-demethyltramadol